485 14 th International Research/Expert Conference ”Trends in the Development of Machinery and Associated Technology” TMT 2010, Mediterranean Cruise, 11-18 September 2010 CHARACTERISTICS OF NON-STATIONARY THERMAL STRESSES IN THE DISC OF THE LAST TURBINE STAGE Zvonimir Guzović, Stanislav Sviderek, Tihomir Mihalić Faculty of Mechanical Engineering and Naval Architecture Ivana Lučića 5, 10000 Zagreb Croatia ABSTRACT In the paper “Modelling of Non-stationary Thermal Stresses in Steam Turbine Rotors” [1] presented on TMT 2004, the algorithm and the results of non-stationary thermal stresses modelling in steam turbine rotor by means of the users software package are shown. Non-stationary thermal stresses are stipulated by pressure change on turbine exit. The results of non-stationary thermal stresses calculations (i.e. of modelling) show on several characteristic regions of the rotor thermal stressed state: a) the rotor central bore; b) the low-pressure rotor; c) the disc of the last turbine stage, and d) the rear-end labyrinth gland. Due to in the paper “Characteristics of Non-Stationary Thermal Stresses in Steam Turbine Rotors” [2] presented on TMT 2006, these characteristic regions are additionally analysed. As in the disc of the last turbine stage the high gradients of thermal and mechanical quantities (temperature, heat flux, deformation, stress) are determined, so this region of rotor is analysed in detail. In this paper the results of this analyse are presented. Key words: steam turbine disc, non-stationary thermal stresses, numerical modelling 1. INTRODUCTION The influence of the exit pressure change on thermal stressed state of the turbine rotor is most evident on the disc of the turbine last stage, since all changes on the turbine exit are manifested first on its work. Therefore, in this paper thermal stressed state in the disc of the last turbine stage (marked as 21 st on the cross section of steam turbine of 30 MW power in Figure 1) is analysed. The moving blades from the 2 nd to 8 th stage are located on a drum-type rotor, while all the remaining moving blades of other stages (1 st , 9 th to 21 st ) are located on discs which have been forged together with the shaft. Therefore the rotor of the analysed steam turbine has been designed as a mono-block (of a single piece) with the central bore. Figure 1. Cross section of steam turbine of 30 MW power